Steam turbine working with wet steam



Feb. 7, 1939.. U, ME|N|NHAUS 2,145,886

STEAM TURBINE WORKING WITH WET STEAM Filed March` 7, 1935 y 2 sheets-sheet 1 Feb. 7, 1939. u. MEININGHAUS I 2,145,886

STEAM TURBINE WORKING WITH WET STEAM Filed lMarch 7. 1955 2 sheets-sheet 2 kPatented Feb. 7, 1939 2.145.886 Y STEAM TURBINE WORKING WET -STEAMi Ulrich Meninghaus, Muelheimfuhr.. Germany Application March r, 1935; snm; No. 9,125 In GermanyAprii 24311934;

s. claims.v (ci. 252-165) Myinvention relates to steam* turbines which includea stage working'with wet steam and more particularly to- .the low pressure 4bladingof such turbines, especially of turbinesifor vlarge quanti-r f .5'1ties of stearnl of high initial pressure or great ,heat-dropf 'The-object of my' invention is toV ldiminish oreliminate theerosion of the blades t impi-nged'by thevwet steam.

` y' 'Phe'water drops contained' inl wet steam are not 1K0 I' capable of following the sudden acceleration inn-y parted'tothe steam itselfY in vthe blade channels. y Theyfdonot, thex-eforejattainL the sameihigh yvelocity as the steam, i. e. their" velocity of ow c' is lower than the velocity of flowlc of the steam.

i, l5' If' the ratio of thefcircinnferential speed w tothe y steam Velocity cvis chosen close to unitye-as has tol be done, for instance, at the blade tips of flow steam turbines'v with highcircumferential' speeds andlongf blades-the ratio u/c (circum- Y 20 ferential speed to the velocity'oiV the water drops) 1 exceeds unity andthewater drops will hit theA reary side of the bladesr with heavy impact caus-,

ing erosion. There is no way of avoiding this drawbackeffectivelywi-tl long axial flow blad'es'ol.'l high circumferential velocity becausel the ratio u/c cannot be diminished without great sacrice of eiciency-in view of the low ratio u/c already prevailing at theblade'roots ywhere the circumferentialspe'edis oftenA only 60% of the circumy ferential speed atfthe'blade tips. f

yWith theobject of' diminishing or eli 'natingf y erosion'of thel'blades or of allowing for a higher degree of humidity.y ofthe 'steam with the same rate of erosionlpropose to` arrange the low press sure blades in the region of humidity in radiallyy traversed kblade "rings `with inlet edges running in an axial direction, the circumferential speed oi 1 each of such bladevv rings relatively tothe circum-r lferential speed of the next following'blade ring l 40 being. less than 85% of the steam velocity in said` blade' rings.

-The invention is illustrated by way of example on the accompanying drawings wherein e Fig; 1 shows va section through a steam turbine 45 ,with a, singievrotatmgfhigh pressure part, double rrotating medium pressure part, and a single rotat- V`ir`1g,zr single flow low pressure part, and

Eig. 2 shows a rsection through an alternative f xdesign of the .medium and low pressurepart f wherein the single.rotatingv low Vpressure part is f constructed according. to the double'v flow prin-` .'ciple, j Y.

. Fig. 3showsz-a fragmentary section through the wet fsteam blading,

y Vlil kIrifEig. Itho-numerals] and2. represent coun-I '2' carries such a disc onlyon the stubv end shown in Fig; I, rtlfle'other-fstub end of the shaft '41 being usedto drivethe exciter, the governor, and the oil (not shown)- for'both generators which electrically Acoupled with each other. The 10 shafts. 3. and are supported in the bearings 5. The. steamV enters at t into the high pressure housing 't andows successively through the radially* traversed blade rows of the two discs 8y and 9 which rotate at 3000 R. P. M. and cooperate with 15 the statici-:aryv4 discs I' and II. The rotational speedof 30001 R. P. M. and the small diameters are: welt adapted to expand the small volume of the vhigh pressure steam with high emciency at lowvelocitlesA and without labyrinth losses. The 20 partly expanded steam is led to the counter running-medium pressure part of the turbine through the pipe lit.- As the steam pressure is already diminished at this: point` and the steam volume accordinglyfincreased the labyrinth losses due to 25.-

the running principle are not of great inuence andi they high relative lspeed of rotation of the counterrunning rotors provides for eilicient expansion of a great part of the pressure head within small space. 'I'he counterrunning is ef- 30 iected by rotating the disc I3 at 3000 R. P. M. in

the'onedirection and rotating the disc I4 at 1500 Rz P. M. inf the other direction. The relative speed of rotation, therefore, amounts to 4500 R. P. M.

'lhefdoubierotating-prlnciple requires 3 labyrinth 35y tional1 thrusty bearing (not shown) for equalzing said, thrust is required. The thrust of the disc Itisl balanced by the sum of the thrusts of the discsfl and 9.,

Accordingto my invention,y the inlet edges of 45 the blades I3! and I9 fixed to the discs I8 and I9 vrun 'in axialfdirection and the relative circumferential speed of` said bladesrelatve to the circumferential speed of. the next following blade ring is diminishedbelow a value corresponding to 85% 5o of the velocity in said blades. In the example shown in Fig. r1 the diminution of the circumferentialspeed of. .the blades fixed to the discs IBfaud i9 relatively to each other is accomplished byv partei the blades on the stationary disc I9 while the discs carrying the blades ahead of said blades run both in opposite direction. In this way, the circumferential velocity of the blades fixed on discs IB and I9 relatively to each other along the whole length ofthe blades is considerably smaller than the steam velocity in said blades, at least smaller than 85% of said steam velocity. Without any abrupt vchange the steam velocity occurring, i. e. without y abrupt change of the blade area, the steam velocity c suddenly becomes far greater than the circumferential speed atv the point of leaving the blading of the discsI3-and III'land entering the bieding of the discs Ia and I9. Thel water drops developing in the blading of the discs I8 and I9 are accelerated up to a velocity about equalto the circumferential speedwithout idifflA culty and any impact on the rear side of the blades is avoided. As the rotational speed decreases from the relative amount of 4500 R. P. M.' to 1500 R. P. M. .at this point I nd it of advantage to diminish the steam velocity simultaneously toa certain amount.

the circumferential speed which progressively increases with the outward flow of the steam and to; keep the ratio u/c below the limit given above.. A; less abrupt change in the relative circumferen. tial speed would be obtained if both generators. I and 2 were to rotate at 1500 R. P. M., but theV work done in the high pressure and the medium pressure parts would be lower. The arrangement chos-en offers special advantages as regards dividing the work between the turbine. Y l

In Fig. 2, the corresponding parts are desigf nated by the same reference numbers.' As the different parts of the turbine shown in Fig. 2 is designed ,for verylarge steam volumes the blading of the discs i3;

and i4 is divided into two parallel blade channels to avoid an excessive length of the blades.

The blading of the discs I8 and I9 is divided in the same way. To provide for a diminution of the steam velocity at the entrance of such blad-- ing and to render possible a further' increase in the blade area in the later stages, about V,half of the steam is taken olf before the steam enters' Y the blading of thediscs I8 and I9 and is led through pipe 20,1110 the blading on discs I 8a and I9a at the other end of the generator 2 whichV blading is similar to the Yblading of the -discs I8, and I9. The blading of thediscs Iafand Illia, is traversed in parallel flow'to the blading Yof the' discs I 8 and i9 and as each vof the bladings has two passages, four parallel passages areoffered to the steam, allowing for ample flow area even for great steam volumes. The thrustsof the discs I3 and ma are opposed vand balance eachother. The high pressure part at the left stub end of the shaft 3 is not shown in Fig. 2,.but may beas-` sumed to be like the arrangement shown in Fig.. 1.` The reduced relative-speed of the blading with reference to the wet steam can be accomplished in various ways. Primarily, the constructonfis' such that the totality of the blade channels lor constrictions' 2l (Fig. 3) Yare made smaller than heretofore for the same conditions of operation.V

In this way higher steam velocities are obtained and correspondingly higher pressure drops -per stage, the numberof blade rings lrequired for the expansion of the wet steam being'jyof course," reduced for a given circumferential velocity. Substantially the same result may,however, be obtained by keeping the number of' blade rings 'Xedf (that is, the'same asin prior turbines operating This gives'at the same'timev sufficient freedom to adapt the steam velocity to under the same conditions), and reducing the diameter of the rings and hence their circumferential velocity, or the rotations per minute can be reduced. Whichever of these measures is resorted to, care should be taken that the velocity of the wet steam in the blading should be morethan about 18% greater than the relative circumferential speed of the blading, regardless of whether one set of blade rings is fixed or runs oppositely to the other set of blade rings.

`By using blades with inlet edges running in axial direction as shown in Figs. 1 and 2, the adk vantage is-obtained that the value of the circumf ferential speed u is constant along the total length of the inlet edges. It is, therefore, possible vto choose throughout the whole length of the blades acircumferential speed u which allows thesteam velocity c along the whole length of the blades to be kept just so much higher than such circumferential speed'as is sufioient to accelerate the Water drops enough to prevent erosion and yet obtain a fair efficiency for the flow of the steam. Doing away with the braking effect of the water drops will more than outweight the small sacri-.

fice in the efciency of the steam flow. With axial flow blades the circumferential speed at the blade tips is up tov almost 70% higher than at the blade roots. to unity at the blade tips to allow at least for eiiicient flow of the steam (no regard being paid to erosion or the braking effect caused by the water drops) the ratio u/c at the blade roots may other parts at theblades, especially at the roots i of thevblades.r Furthermore, the great heat drop inthe last blade rows which usually run with high circumferential speeds (up to 400 m/sec.) causes a very rapid expansion of the steam and requires, therefore, an abrupt increase in flow area from blade row to blade row. The larger the blade length, the larger the increment of the length for the same ratio of expansion, the required increment exceeding mostly the value permissible in View of efficient steam flow. The increment is, therefore, Aoften restricted Vand such restriction causes the steam velocity to decrease in the stages preceding the last stage if the steam velocity in the last stage is not to exceed a maximum value. As the circumferential speeds of ad jacent axial flow stages are substantially equal, the value of u/c must necessarily drop in the preceding stages thus promoting erosion and braking effect in such stages. VIt is a well known fact that the erosion is often found to be worst at the blade tips or close to the blade tips of the stages preceding the last one. Radial flow blading adapts the circumferential Yspeed to the decrease in the steam velocity in the preceding stages and allows-at least if rotating blades cooperate with stationary blades-for ample possibility of Vincreasing the steam velocity'in the If the ratio u/c is made closeV last stage, whereas aXial flow blading or counteri of the blades I8, I9 is obtained, as ywill be readily understood by suitable design of the blade rings whereby the necessary constrictions are provided "in the'path of the steam, the blading being designed in known manner in accordance with the y volume of steam passing per unit of time which in turn depends upon the degree of expansion, the

, pressure, the temperature and the weight of steam per unit of jtime.

pThepresent invention, as will be clear from the above, contemplates directing substantiallyr all of the steam which has reached the wet condition, following its partial expansion, into a radial ilowturbine having the relative speed described hereinbefore. In plants employing intermediate superheating wherein wet steam is converted to l the'dry condition, the steam'may leave the plant in the dry state. In such a plant the present invention may be taken advantage of in the stage rutilizing Vthe wet steam vimmediately in advance y 130 of the superheating. It will thus be apparent that Y the present invention is not limited in its application to the very last stage of the plant, but may V be incorporated in a turbine stage employing wet steam either before the superheating orafterthe y 35 superheating. y

' f- Ikclaim:

r1. A steam turbine plant wherein steam is exbanded from a substantially dry state to the wet 'state containing droplets of condensed moisture, comprising a casing, a shaft journaled in the l casing, rotating blade-carrying discs mounted on f )said shaft, an inlet Yfor dry steam under pressure f kleading to said discs, stationary discs fixed to said i casing, radially traversed rotating Yblades with entrance edgesrunning in axial direction disposed to be impinged by wet steam and supported bythe rotating discs, and stationary blades alternating with saidA rotating blades and supportedwithin the casing, said rotating Iblades being grouped into lblade rings providing channels in the path for ythe steam,said channelsbeing so dimensioned and the number, diameters andnormal speed of revolutions ofthe rotating rings being so determined asto compel the steam to attain in the blades 55 avelocity relative to the blades which is more thanabout 18% above the circumferential speed y of `rotating blades relative to the stationary blades.

2. A steam turbine plant wherein .steamV is ex- 60 panded from a substantially dry state to the wet state containing droplets of condensed moisture, comprising a casing, two shafts journaled in the casing, rotating blade-carrying discs mounted for rotation in opposite directions on said shafts, an

65 inlet for dry steam under pressure leading to said discs, the blading on certain of said discs being disposed to be traversed by the steam while it is in the substantially dry state, radially traversed Vblades with entrance edges running in axial di- 70 rection disposed to be traversed by the steam after it has been expanded to the wet state in the first-mentioned blades and supported by certain of said discs, an-d radially traversed blades alternating and cooperating with the aforementioned 75 radially traversed blades, said Aradially traversed bladeszfhavingfa diierent rated "relative speed of rotation than :the :mst-.mentioned blades.

.3.. Agsteamfiturbine plant wherein steam is expandedzfrorn falsubstant-ially dry :state to the wet stategcontaining droplets of .condensed moisture, Qmprisng,-a.ca'sing,f twoshaftsijournaled in the casing afar :rotationfin opposite directions, discs mounted on the shafts for rotation therewith, stationary discs xed to said casing, alternating rings of blades mounted on said discs and disposed to be traversed by the steam while it is in the substantially 4dry state, and radially traversed rotating and stationary blades with entrance edges running in axial direction mounted on said rotating and stationary discs, respectively, and arranged to be traversed by the steam after it has been expanded to the wet state in the firstmentioned blades, said last-mentioned rotating and stationary blades having a lower rated relative lspeed than the first-mentioned blades, and an inlet for dry steam under pressure leading to the first mentioned rings of blades.

4. A steam turbine plant according to claim 3, wherein the two shafts have different rated speeds of rotation.

I ed to be rst traversed by the steam While it is in the substantially dry state is fixed to the same shaft as the rotating blades adapted to be traversed by the steam after it has been expanded to the wet state in the rst mentioned blades.

'7. A steam turbine plant wherein steam is expanded from a substantially dry state to the wet state containing droplets of condensed moisture, comprising a casing, two shafts rotating in opposite directions at diierent speeds and journalled in saidl casing, rotating discs carrying rings of blades and mounted on said shafts, the disc structure mounted on one of said shafts cooperating with part of the disc structure on the second shaft, and a stationary disc structure carrying rings of blades and xed to said casing and cooperating with the remainder of the said rotating disc structure on the second shaft, the blades on the counterrunning discs being arranged to be traversed by the steam while it is in the substantially dry state, and an inlet for dry steam under pressure leading to said blades, the blades on the stationary disc structure and the rotating blades cooperating therewith being radially traversed with their entrance edges running in axial direction and being disposed to be traversed by the steam after it has been expanded to the Wet state in the blading of said counterrunning discs.

8. A steam turbine plant wherein steam is expanded from a substantially dry state to the wet state containing droplets of condensed moisture, comprising a casing, two shafts journaled in the casing, blade carrying discs mounted on said shafts, an inlet for dry steam under pressure leading to said discs, radially traversed rotating blades with entrance edges running in axial direction adapted to be impinged by partially expanded wet steam and supported by said discs, radially traversed blades alternating and cooperating with the radially traversed rotating blades, said rotating blades being grouped into blade rings providing channels in the path for the, steam, said channels being so dimensoned and the number, diameters and normal speed of revolution of the rotating rings being so determined as to' compel the steam to attain in the blades a velocity relative to said blades Which is more than about 18% above the circumferential speed of the aforementioned rotating blades relative to the blades cooperating with them, Whereby the entrained drops of water are given a kvelocity of the order of said relative circumferential speed and erosion of therblades is reduced or substantially eliminated. Y

ULRICH MEININGI-IAUS. 

